Impact of interproximal groove placement and remaining coronal tooth structure on the fracture resistance of endodontically treated maxillary anterior teeth.

PURPOSE: This in vitro study investigated the effect of grooves, remaining tooth structure, and their combination on tooth fracture resistance of endodontically treated anterior teeth with cast dowel and cores. MATERIALS AND METHODS: Sixty extracted maxillary anterior teeth of similar dimensions were endodontically treated and then randomly divided into three groups of 20 teeth each. The teeth in the first group were cut horizontally at the widest part of their anatomical crowns. Three hundred and sixty degree 1 and 2 mm axial walls for ferrule effect were provided for the teeth in the second and the third groups, respectively. Cast dowel and cores were fabricated for all teeth. Each group was then subdivided in two groups: one with no grooves and another with mesial and distal grooves. Hence, six groups were created as follows: (1) teeth with no remaining coronal tooth structure and no grooves (group A-control); (2) teeth with no remaining coronal tooth structure, with mesial and distal grooves (group B); (3) teeth with 1 mm remaining coronal tooth structure, with no grooves (group C); (4) teeth with 1 mm remaining coronal tooth structure, with mesial and distal grooves (group D); (5) teeth with 2 mm remaining coronal tooth structure and no grooves (group E); and (6) teeth with 2 mm remaining coronal tooth structure, with mesial and distal grooves (group F). Complete cast crowns were then fabricated for all teeth. A universal testing machine applied controlled loads to the teeth at a crosshead speed of 2.54 mm/min at an angle of 130 degrees to the long axes of the teeth until failure occurred. The loads were applied 2 mm lower than the incisal edges of the specimens. Descriptive statistics, one-way ANOVA (alpha= 0.05) and Tukey's honestly significant difference (HSD) tests were used to determine the effect of failure loads among the tested groups (alpha= 0.05). RESULTS: The mean failure loads were (N): group A (control), 151.21 +/- 38.18; group B, 221.53 +/- 107.03; group C, 295.35 +/- 81.92; group D, 270.20 +/- 76.01; group E, 491.70 +/- 180.36; group F, 432.67 +/- 193.83. Group E presented the highest failure load and group A (control) the lowest. CONCLUSION: The inclusion of interproximal grooves on the cast dowel and cores of endodontically treated anterior teeth with 1-2 mm of remaining coronal tooth structure does not significantly lower the failure threshold.